Known in the prior art are contrivances for combined machining of internal cylindrical surfaces with a double-tool "floating" block and a multiple-roller planetary deforming head. These contrivances make it possible to machine the cylindrical surfaces with comparatively high accuracy and quality of machining only using comparatively precise blanks having permissible variations of the stock to be removed not exceeding 0.1-0.15 mm ("Hegenshaidt", FRG, Machine Tools-86).
The use of such known combination contrivances involve a preliminary machining of the external surface of a part which complicates the manufacturing process and makes it more labour-intensive.
Also known in the prior art is a contrivance for the cutting-deforming of external cylindrical surfaces in a housing whereof there are arranged in succession a head with deforming rollers and a tool-holder. The tool-holder is installed in the housing for movement ("floating") in a plane perpendicular to the direction of a longitudinal feed. The tool-holder has an opening for passing a workpiece to be machined and one pair of cutting tools are secured therein with the noses thereof disposed oppositely in relation to the cylindrical surface of a part under machining (U.S. Pat. No. 4,393,675).
The contrivance described hereinbefore makes it possible to machine the external cylindrical surface of a part with a comparatively high productivity at the expense of a comparatively high rigidity of the tool-holder. However,the cylindrical surfaces of machine parts machined by means of this contrivance suffer from waviness which is not to be tolerated in the machining of cylindrical surfaces of the parts the accuracy and surface quality of which should meet stringent requirements.
Waviness results from variations in the value of the stock removed by the oppositely arranged cutting tools caused by a change in the position of the axis of rotation of the workpiece being machined and also by increasing friction and inertia forces obstructing the radial displacement ("floating") of the tool-holder.
In a number of cases after machining by the cutting action the workpiece, for example, a shaft comprises cylindrical sections of the equal diameter and correct shape but with the axes of symmetry displaced relative to one another. When such sections of the shaft are subjected to a superficial plastic deformation accomplished by the deforming rollers the latter smooth out the surface microroughness, follow the defects and in case of resonance effects occurring when the deforming rollers pass over each transition section of the shaft they increase the waviness.
Besides, the design embodiment of the tool-holder fails to ensure the maximum stability thereof relative to the cylindrical surface under machining. The maximum stability of a tool-holder is understood as a positional stability of a size-forming tool (roughing, for example) relative to the axis of rotation of the lathe spindle under any adverse conditions occurring in the process of machining the cylindrical surfaces by the cutting and superficial plastic deformation, and including:
variations in the depth of cutting accomplished, for example, by roughing and finishing tools; PA1 nonstraightness of the axis of a workpiece under machining; PA1 variations in the relative position of the axis of a rest-deforming head and the axis of rotation of a workpiece under machining.